As is well known in the textile field, many fabrics are made from yarn that is composed of a blend of different fibers, including natural and synthetic fibers, and the quality of such fabrics depend to a significant extent upon the uniformity of the blend of the different fibers from which the yarn is made.
The blending of fibers in preparation for yarn formation is commonly carried out by providing a plurality of fiber feeding machines arranged in a bank to deposit measured quantities of fiber onto a conveyor or the like, a typical example of such a system being disclosed in Lytton U.S. Pat. No. Re. 25,609. Each fiber feeding machine generally handles a different type of fiber which is fed within the machine to a weigh pan until a predetermined weight of fiber is collected therein, whereupon pivoted doors at the bottom of the weigh pan are thereafter opened to release the predetermined weight of fiber which falls to a conveyor or the like for transportation with other fiber batches to blending equipment.
Since, as indicated above, the uniformity of the ultimate blend of fibers is important, it will be apparent that the accuracy of the weight of each batch of fiber deposited on the conveyor is quite significant in arriving at a blend having a desired uniformity and predictability. A known method of controlling the accuracy of the weight of fiber deposited onto the conveyor has been to provide a mechanical arrangement by which the weigh pan is mounted at one end of a pivoted arm which includes counterweights mounted at the other end of the arm and movable therealong, whereby when a predetermined weight of fiber, as determined by the position of the counterweights on the arm, is collected in the weigh pan, the arm will pivot and thereby operate an electrical switch that stops further feeding of fiber to the weigh pan. Typical examples of mechanical arrangements of the foregoing types are disclosed in greater detail in the above-mentioned Lytton U.S. Pat. No. Re. 25,609 and Lytton U.S. Pat. No. 3,196,967.
While such mechanical arrangements provide a reasonable degree of control for the weight of fiber which are ultimately delivered to the blending equipment, such arrangements also have certain drawbacks in terms of the accuracy and uniformity of the actual fiber weight which is released from the fiber feeding equipment during each fiber release cycle. More specifically, the pivoted arm and movable counterweight arrangement presents inherent mechanical tolerances which may make it difficult to obtain a generally precise weight setting for the collected fiber in the weigh pan. Moreover, since the weigh pan itself is mounted at the end of the pivoted arm, any fly or fiber which attaches itself to the weigh pan or the components associated therewith will offset to some extent the effect of the counterweights whereby the arm will pivot before the desired weight of fiber has been collected in the weigh pan. Similarly, it is not uncommon for a portion of the collected fiber in the weigh pan to cling to the interior walls thereof and not fall from the weigh pan when the doors are opened to release the fiber, and it will be apparent that this clinging fiber may reduce the weight of fiber dumped during a given cycle.
Another method for weighing fibers is also disclosed in Grayson U.S. Pat. No. 4,137,976, which is directed primarily to a system for forming a plurality of bales of fiber, each of which has a uniform total weight so that sellers and buyers of staple textile fiber will know substantially the exact weight measure of each bale and the total weight of fiber transferred in any particular transaction. In this system, cut textile tow is delivered to a baling press or the like in a succession of batches, each batch being cyclically collected in and dumped from a container. The container is arranged with a load cell that measures the cumulative weight of the container and the fiber collected therein and generates signals indicative of the fiber weight in the container, and this signal is transmitted to an electronic control system, including a microprocessor unit, which stops the feeding of fiber to the container when a predetermined fiber weight has been reached, and which provides a total of all of the actual fiber weight released from the container in preceding cycles and adjusts the weight of fiber released in subsequent cycles for the purpose of controlling the total weight of fiber delivered to the baling press, whereby each bale formed by this system will have a generally uniform and predetermined total weight.
Thus, the foregoing system, insofar as it measures the actual weight of the fiber released from the container, overcomes some of the aforementioned drawbacks associated with the mechanical arm and counterweight arrangement, but such system automatically varies the fiber weight released during each cycle solely in response to differences between the actual cumulative total weight of fiber theretofor delivered from the container and the predetermined cumulative total weight which is desired to be delivered in connection with the formation of a bale having an accurate and predictable total weight. While this total weight concept may have advantages in carrying out the intended purpose of the Grayson invention, namely the formation of bales having a uniform weight, such concept would have practical limitations if applied to continuous blending systems where the emphasis is on continuously delivering a series of fiber batches, each of which is substantially equal in weight to the other batches delivered to the blending line.